A subject of the present invention is a method and a device for adjusting a weather vane. Another subject is a weather vane that can be adjusted by this method. A weather vane is a device for measuring wind direction. The invention finds a more particular application in the aeronautical industry, where the adjustment of a weather vane is of vital importance. This is because the value of the measurement of the apparent wind direction for an aircraft makes it possible, after calculation, to obtain the value of incidence and lift parameters. These two parameters need to be known reliably because they allow optimum flight conditions to be ensured, but above all these are parameters which are critical to flight safety. The method of the invention can nonetheless be used in other fields, particularly in meteorology. Weather vanes installed at meteorological stations have also to be adjusted regularly, or even changed.
A weather vane is a member, part of which is external. This external part is subjected to climatic variations, particularly to temperature variations. In addition, it may become damaged by impact with external bodies, such as birds, grains of sand or bits of ice. More generally, it may become worn by external forces that may be applied to it. The conditions external to an aircraft are very harsh. The part of the weather vane that is directly sensitive to the wind is delicate. Forces applied to this device in the flight phase are very strong. These forces may also alter the adjustment of the wind-sensitive part with respect to orientation sensors to which it is connected.
For economical reasons, when the weather vane has to be replaced, only a limited part thereof is replaced. A weather vane thus comprises a vane that can move in the wind, a sensor support and a probe body. Sometimes only the vane hanged. A new vane has then to be fixed to a sensor support and to a probe body already in place, or a new vane and a new sensor support have then to be fixed to a probe body already in place. In such cases, there is a need for the orientation sensors to be adjusted on site with respect to the probe body, to suit the new weather vane thus formed.
Furthermore, airlines impose frequent checks on the adjustments. These checks may sometimes result in drifts being observed and therefore lead to the weather vane having to be readjusted. It would therefore seem necessary to implement a reliable and economical method for adjusting the weather vane.
The most accurate method of adjustment involves adjusting the weather vane by putting it in a wind tunnel. What happens is that the wind tunnel makes it possible to create wind whose direction is perfectly known. A complete weather vane is then adjusted directly according to the direction of the wind provided by the wind tunnel. Under these conditions, a complete weather vane placed on the aircraft is perfectly adjusted.
Now, a system of adjusting weather vanes in a wind tunnel is very expensive. In particular, it requires special infrastructures in which air streams created have a controlled direction. Furthermore, this system is lengthy to implement because the adjusting time is longer in this case. This type of control also involves grounding the aircraft for the duration of the control, and the time that an aircraft spends grounded is also expensive.
Nonetheless, this type of adjustment is feasible for industrial designers or weather vane repair companies who have the means of amortizing the investment in an incidence wind tunnel.
A weather vane is made up of a mechanical wind-sensitive part, the vane and of orientation sensors. The orientation sensors are placed on a probe body via a sensor support. Adjustment is performed by fixing the vane in a known position with respect to the probe body, and by mechanically adjusting the position of the sensor support with respect to this probe body, so that a signal delivered by the sensors in the known vane position has an expected value.
In the state of the art, placing the vane in a known position with respect to the probe body entails the existence and material identification on the vane of a mark corresponding to an aerodynamic zero. The aerodynamic zero is observed in the wind tunnel. It corresponds to the vane being oriented along the axis of the wind from the wind tunnel, and to a corresponding position of the sensor support which, in this case, gives an expected measurement signal (generally a null signal). For this aerodynamic zero, the relative positions of the vane with respect to the sensor support are definitively marked. In practice, this marking is achieved by marking the vane with respect to the probe body and by also marking the sensor support with respect to the probe body. The aerodynamic zero is identified by a hole, made at the factory, in the vane. The precision with which this hole is centered with respect to the theoretical location observed in the wind tunnel is a first error. This first error is known as the precision error.
The principle of adjustment, in the state of the art, is to fix the hole representing the aerodynamic zero in a known position with respect to the probe body, and to place the orientation sensor, with respect to this fixed assembly, in a position such that the measurement signal delivered is the expected measurement signal (generally the null signal). The problem with this type of adjustment is that of getting the fixed assembly, in a reference position, of the probe body and of the vane the same each time during successive adjustments. Because of these multiple interventions, the hole becomes deformed and enlarged. The deformation over time of the hole that symbolizes the aerodynamic zero creates a second type of error. This second type of error is variable over time and is therefore known as the adjustment repeatability error. What happens is that the deformation of this hole leads to the probe body and wind-sensitive part being fixed in varying positions even though this assembly is supposed to be fixed in a unique reference position.
It is an object of the present invention to solve the precision and repeatability errors of the known method of adjusting weather vanes. The subject of the invention is a method for adjusting a weather vane. The principle of adjustment is based on a succession of four steps.
A first step consists in placing the vane, orientation sensor support and probe body assembly in a known and fixed position, using a setting rig. The sensor support and the probe body which are used in this case may be unique factory supports and bodies used for all the vanes manufactured and requiring adjustment. In the fixed position, the sensor support is fixed to the probe body. This assembly is itself fixed to the setting rig. The vane of the weather vane is then pushed against a beam of this rig. A first value of the signal delivered by the sensors, known as the mechanical zero angle, is then measured.
A second step consists in placing this entire device, with the same fixed relative arrangement of the sensor support and of the probe body, on a second setting rig, leaving the vane free to move. During this second step, the vane is subjected to wind from a wind tunnel producing wind whose direction is known with respect to the fixed assembly, and oriented in a direction that is known with respect to the second setting rig. A second value of the signal delivered by the sensors and known as the aerodynamic zero angle is then measured.
During these first two steps, a difference is observed between the signals delivered by the orientation sensors. This difference between the signals delivered is equivalent to an angle through which the vane has turned. This difference is known as the angular difference between the mechanical zero and the aerodynamic zero. In a third step, the value of this angle is recorded on a document that accompanies the vane, or on the vane itself. This angle will then allow the rotation sensors to be adjusted quickly according to the specifics of the mounted vane.
A last step is the only one to be performed on site when a new vane is being adjusted on an existing probe body and orientation sensors assembly, or when readjusting a weather vane.
During the last step, which corresponds strictly to the adjusting action, the vane and the probe body are fixed in a position identical to that of the first step. To do this, a setting rig in every respect identical to the setting rig used in the first step is used on site for adjustment. Adjustment consists then in turning the sensor support about an axis of rotation of the vane with respect to the probe body. This adjustment is performed by measuring the signal produced by the sensors. A sensor support position with respect to the probe body for which the measured signal is equal to the difference between the signals delivered during the first two steps, namely to the angular difference, is adopted. In this case, the weather vane is adjusted with the measurement precision of these sensors, which is far better than the optical or mechanical precision of alignment of a hole as used in the state of the art.
A subject of the invention is therefore a method for adjusting a weather vane in which
the weather vane is placed, on site, in a site setting rig, and
the position of an orientation sensor that senses the orientation of the weather vane with respect to a probe body of the weather vane and with respect to a vane of the weather vane is mechanically adjusted, characterized in that:
at the factory, the respective positions of the orientation sensor and of the probe body are fixed in a reference relationship,
the probe body is placed on a first factory setting rig,
the vane is kept in a sustained position which is mechanically known with respect to the first factory setting rig, and a first signal (mechanical zero) delivered by the orientation sensor for this vane position is measured,
the weather vane, maintaining the same reference relationship, is subjected to a wind, obtained by a wind tunnel, of known direction with respect to the first setting rig, and a second signal (aerodynamic zero) delivered by the orientation sensor for a vane position corresponding to this wind of known direction is measured,
on site, the probe body is placed on a site setting rig identical to the first factory setting rig, the vane is put back in the same sustained position with respect to the site setting rig, and a third signal delivered by the orientation sensor for this sustained vane position is measured
the position of the orientation sensor is mechanically adjusted so that the third signal is equal to a difference between the first and second signals (angular difference).
As an alternative, instead of using an orientation sensor measurement instrument, an offset of the sensor body so that angularly this offset is equal to an angular difference deduced or measured from the previous two measurements is measured, on site, during the third step. A subject of the invention is then a method for adjusting a weather vane in which:
the weather vane is placed, on site, in a site setting rig, and
the position of an orientation sensor that senses the orientation of the weather vane with respect to a probe body of the weather vane and with reference to a vane of the weather vane is mechanically adjusted, characterized in that:
at the factory, the respective positions of the orientation sensor and of the probe body are fixed in a reference relationship,
the probe body is placed on a first factory setting rig,
the vane is kept in a sustained position which is mechanically known with respect to the first factory setting rig, and a first angular signal delivered by the orientation sensor for this vane position is measured,
the weather vane, maintaining the same reference relationship, is subjected to a wind, obtained by a wind tunnel, of known direction with respect to the first setting rig, and a second angular signal delivered by the orientation sensor for a vane position corresponding to this wind of known direction is measured,
on site, the probe body is placed on a site setting rig identical to the first factory setting rig, the vane is put back in the same sustained position with respect to the site setting rig, and the orientation sensor is offset with respect to the probe body so that an offset angle of a reference of the orientation sensor with respect to a reference of the probe body is equal to the difference between the two angular signals.
Another subject of the invention is a device for adjusting a weather vane for measuring the direction of the wind, this weather vane comprising a wind-sensitive vane, secured to a shaft supporting an indicator pointing to an orientation sensor mounted on a sensor support plate, and a probe body, this plate being orientable with respect to the probe body, characterized in that it comprises, for each weather vane, a label for adjusting the plate with respect to the probe body and with respect to the vane once the weather vane is mounted in a setting rig.
Furthermore, the sensor support generally has two rotary sensors driven by the axis of rotation of the vane. For a normal angle of incidence of the wind on the vane (directed more or less along the aircraft fuselage), the two sensors are placed laterally one on each side of this axis of rotation. It would seem that the play of the original axis of rotation, which increases little by little on the axis of rotation of the vane, leads to the indications supplied by the two sensors becoming misadjusted. This misadjustment is all the more difficult to combat as the play of the axis of rotation of the vane remains and changes over time.
The invention seeks to abort the detrimental consequences of this play that cannot be eliminated unless the guides for the vane axis are changed very frequently. The invention has chosen to locate the two rotary sensors in line with the axis of rotation which has the most frequent (or most critical) wind direction. In this position, the play of the axis of rotation remains but its effects are neutralized: the indications supplied by the sensors do not contain error. For another wind direction, but one which corresponds to a less frequent (or less critical) angle of incidence of the wind, the indications are still slightly erroneous, but this is less troublesome because it is less frequent or less critical.
Another subject of the invention is therefore a weather vane for measuring wind direction, comprising a wind-sensitive vane secured to a rotary shaft and driving a measurement member which comprises a set of sensors, each sensor rotating about an axis parallel to the rotary shaft, characterized in that the axes of the sensors are situated in a plane passing through a leading edge of the vane and the rotation shaft of the vane for a main position of the weather vane.